Show more specific error messages when forking a project

What does this MR do and why?

Show more specific error messages in a fork form

Display error messages coming from server when possible

Changelog: changed

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Try forking a project with a name/namespace/path of already existing fork Or with a user which don't have enough access rules

Related to #430214 (closed)